Stent delivery system

ABSTRACT

The present invention relates to a system for delivering a medical prosthesis into a body lumen. A preferred embodiment of the invention utilizes a catheter having a stent mounted at the distal end that is released into the body lumen by movement of an outer sheath covering the stent in the proximal direction. The stent expands to conform to the inner wall of the lumen and the catheter is withdrawn.

RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/052,214 filed on Mar. 31, 1998, the entire teachings ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Implantable medical prostheses, such as stents, are placed within thebody to maintain and/or treat a body lumen that has been impaired oroccluded, for example, by a tumor. The stent can be formed of strands ofmaterial formed into a tube and are usually delivered into the bodylumen using a catheter. The catheter carries the stent to the desiredsite and the stent is released from the catheter and expands to engagethe inner surface of the lumen.

A self-expanding stent can be made of elastic materials. These are heldin a compressed condition during catheter delivery by, for example, asheath that covers the compressed stent. Upon reaching the desired site,the sheath constraining the stent is pulled proximally, while the stentis held in the desired position such that the stent expands.

There are both self-expanding and non-self-expanding stents. Theself-expanding type of device is made with a material having an elasticrestoring force, whereas a non-self-expanding stent is often made withelastic, plastically deformable material. It is positioned over amechanical expander, such as a balloon, which can be inflated to forcethe prosthesis radially outward once the desired site is reached.

SUMMARY OF THE INVENTION

In a preferred embodiment, the invention features an implantable medicalstent having a low profile during delivery. The stent is a tubular bodywith a body wall structure having a geometric pattern of cells definedby a series of elongated strands extending to regions of intersection.An example of a stent having a cell shape in accordance with theinvention can be found in U.S. Pat. No. 5,800,519, which issued on Sep.1, 1998, the entire contents of which is incorporated herein byreference. This stent cell structure utilized helically wrapped jointsto connect the different strands to form a tubular body.

A limitation on the use of the helically joined stent involved theminimum constrained diameter of the stent during delivery. Because ofthe helically wrapped joints abutting one another along a givencircumference, the minimum constrained diameter of the stent was 9French (3 mm). For example, the length of the helically wrapped jointfor a strand having a diameter of 0.006 inches (0.15 mm) in theconstrained position is 0.045 inches (1.1 mm). For a five cell structurehaving five helically twisted abutting joints, this results in aconstrained circumference of 0.228 inches (5.79 mm) with a diameter of0.072 inches (1.8 mm). However, there are many applications in which itis necessary to achieve a smaller constrained diameter to providedelivery, for example, through smaller lumens within the vascularsystem, to reduce trauma during percutaneous delivery, or to provideendoscopic delivery through small diameter channels of endoscopes.

To achieve a smaller constrained diameter of 8 French or less, forexample, a preferred embodiment of the invention replaces one or more ofthe helically wrapped joints along any given circumference with a simplecrossed joint in which one strand crosses either above or below a secondstrand. Thus, the strands at a crossed joint can move more freelyrelative to each other, but this structure reduces the minimumcircumference as the length of one or more helically twisted joints hasbeen removed. This can reduce the constrained diameter by 50%.

In another preferred embodiment of the invention, the stent can includea first tubular body made from a first group of strands and a secondtubular body surrounding the first tubular body and made from a secondgroup of strands. This type of structure can be used to fabricate alow-profile device having sufficient radial expansion force for aself-expanding stent without a substantial change in foreshortening.This embodiment can include, for example, three or four helicallywrapped joints along any circumference of the first and second tubularbodies in which the joints of the two bodies are offset in theconstrained state. This embodiment also significantly improves the ratioof the expanded diameter to the constrained diameter.

The strands of the first group can have a different shape, diameter, ormaterial from the strands of the second group such that the inner bodyhas a larger radial restoring force than the outer body and can therebyimpart the outward force to the outer body.

In one embodiment, the strands of the inner body can be thicker than thestrands of the outer body and can be interleaved with the outer bodyalong the entire length of the stent. In another preferred embodiment,the inner and outer bodies can be interlocked at one or both ends. Thiscan permit the use of a cover between the inner and outer bodies along acertain portion of the stent. The use of the cover can enhanceepithialization between the wall of the lumen and the outer body, reducemigration of the stent in certain applications and can prevent tumorin-growth. The cover can also provide a supporting matrix for drugdelivery.

In one preferred embodiment, the strands of the stent are woven in apattern with interlocking joints and skip joints as discussed above. Inaddition, the adjoining ends of the stent are aligned parallel to eachother and laser-welded to secure the adjoining ends of the stent. Thewelded ends allow the stent to be compressed to a low profile.

In one preferred delivery system, the stent is positioned over an innershaft and is covered by a composite sheath. The composite sheath cancomprise a plurality of materials to provide a variable property such asa graded stiffness along the length of the sheath. In one embodiment thesheath can include a braid or coil between outer and inner sheath layersto provide the longitudinal stiffness and flexibility needed forparticular applications. The sheath can have at least a ten percentvariation in stiffness along its length and as much as a fifty percentvariation with the stiffer section at the proximal end and the leaststiff section at the distal end. The sheath can extend coaxially aboutthe inner shaft from the handle connected to the proximal end of thecatheter and can be connected to an actuator that is manually operatedby the user to slide the sheath relative to the inner shaft.

In one embodiment the inner shaft can include a braided tube, whichextends from the proximal handle to a distal position of the deliverysystem. The inner shaft extends through a lumen of a catheter from theproximal handle to a distance short of the distal end where the catheterends. The inner shaft can be free-floating within the lumen and receivesthe stent at the distal end. An outer sheath overlies the stent and theinner shaft and is moved to release the stent using a pull wire which ismoved by the proximal handle using a conventional tooth strip attachedto a pull wire.

In a preferred embodiment, the inner shaft is formed of steel braidedtube encased in a polyimide. For low profile stent delivery systems,where the smaller diameter of the body lumen or the smaller diameter ofthe endoscope delivery channel necessitate improvements in the push (orpull) strength of the catheter, the use of a braided tube to maintainflexibility and pushability without kinking provides effective deliveryof low profile stents.

In the embodiments described above and in other embodiments, a mountingring can be secured to the inner shaft or braided tube at the stentplatform on which the stent is placed. The mounting ring has at leastone radial member or ridge which projects towards the outer sheath. Theridge is located preferably at the proximal end of the stent. The ridgesextend longitudinally, allowing the stent to be properly positionedwhile also allowing maximum compression of the stent for minimizing thediameter of the delivery system.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1A is a flat layout view along the longitudinal axis of a stent;

FIG. 1B is an enlarged portion of the stent taken at section 1B—1B inFIG. 1A;

FIG. 2A is a perspective view of a stent according to the invention;

FIG. 2B is a flat layout view of an expanded low profile stent of FIG.2A;

FIGS. 2C and 2D are close-up views of their respective portions as shownin FIG. 2A;

FIG. 3 is an enlarged cross-sectional view of a delivery tube containinga low profile diamond metal stent;

FIGS. 4A and 4B illustrate a mandrel for making a stent of FIGS. 2A, 2B,and 3;

FIG. 4C is a sectional view of the strands attached with a ball-welding;

FIG. 4D is a flat layout view of the joining ends of a low profile stentaccording to an alternative embodiment;

FIG. 4E is a perspective view of the strand of the stent in a laserwelding apparatus;

FIG. 4F is a sectional view of the strands laser welded;

FIG. 5A is a distal end view of an endoscope;

FIG. 5B is a sectional view of the distal end of the endoscope;

FIG. 6A is an “over-the-wire” delivery system;

FIG. 6B is an enlarged view of the middle section of the “over-the-wire”delivery system;

FIG. 7 is a rapid exchange delivery system;

FIGS. 8A-8E illustrate the operation of the delivery of the stent;

FIG. 9 is a flat layout view of a double layer stent;

FIG. 10 is a flat layout view of an alternative embodiment of a doublelayer stent;

FIG. 11 is an enlarged cross sectional view of the double layer stent ofFIG. 10 with an interposed cover in an artery;

FIG. 12 is a cross sectional view of the double layer stent with theinterposed cover taken along line 12—12 of FIG. 11;

FIG. 13 illustrates a mandrel for making a stent of FIGS. 9 or 10 and11;

FIG. 14A is a perspective view of an alternative stent having sixstrands; and

FIG. 14B is a flat layout view of the stent of FIG. 14A.

FIGS. 14C and 14D are close-up views of their respective portions asshown in FIG. 14A;

FIG. 15A is a side view with portions broken away of an alternativeembodiment of an “over-the-wire” delivery system;

FIG. 15B is an enlarged view of a middle section of an “over-the-wire”delivery system;

FIG. 15C is an enlarged view of the distal end of an “over-the-wire”delivery system;

FIG. 16A is a sectional view taken along the line 16A—16A of FIG. 15B;

FIG. 16B is a sectional view taken along the line 16B—16B of FIG. 15C;

FIG. 17A is a side view of a portion of the catheter showing a lockingring;

FIG. 17B is a sectional view taken along line 17B—17B of FIG. 17Ashowing the interaction of the locking ring with the stent;

FIG. 17C is an illustration of a partially deployed stent with a lockingring;

FIG. 18 is a sectional view showing an alternative lock ring with thestent;

FIG. 19A is a side view, with portions broken away, of an alternativeembodiment of an “over-the-wire” delivery system;

FIG. 19B is an enlarged view of the distal end of the “over-the-wire”delivery system of 19A;

FIG. 20A is an enlarged view of the distal end of an alternativeembodiment of an “over-the-wire” delivery system;

FIG. 20B is a similar view with the inner shaft removed;

FIG. 20C is a sectional view of the distal end of an “over-the-wire”delivery system; and

FIG. 21 is an enlarged view of an alternative embodiment of an“over-the-wire” delivery system;

FIG. 22A is a flat layout view along the longitudinal axis of a stent;

FIG. 22B is an enlarged portion of the stent taken at section 22B—22B inFIG. 22A;

FIG. 23A is a flat layout view of another embodiment of the stentaccording to the invention;

FIG. 23B is a flat layout view of another embodiment of the stentaccording to the invention;

FIGS. 24A and 24B are oblique views of the nodes of a stent;

FIGS. 25A and 25B illustrate a mandrel for making a stent of FIGS.22A-23B;

FIG. 26A is an enlarged cross-sectional view of a delivery tubecontaining an alternative embodiment of a low profile diamond metalstent;

FIG. 26B is an enlarged portion of the stent taken at section 26B—26B inFIG. 26A;

FIG. 27A is a side view of a coaxial delivery system with portionsbroken away; and

FIG. 27B is a sectional view taken along line 27A—27A of FIG. 27A.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings in detail, where like numerals indicate likeelements, there is illustrated an implantable prosthesis in accordancewith the present invention designated generally as 10.

Medical prostheses, such as a stent 10 according to the invention, areplaced within the body to treat a body lumen that has been impaired oroccluded. Stents according to the invention are formed of wireconfigured into a tube and are usually delivered into the body lumenusing a catheter. The catheter carries the stent in a reduced-size formto the desired site. When the desired location is reached, the stent isreleased from the catheter and expanded so that it engages the lumenwall as explained below.

A stent 20 is shown in a flat layout view in FIG. 1A. The stent 20 isformed of elongated strands 22 such as elastic metal wires. The wires 22are woven to form a pattern of geometric cells 24. The sides 26 a, 26 b,26 c, and 26 d of each of the cells 24 are defined by a series of strandlengths 28 a, 28 b, 28 c, and 28 d. Each of the sides 26 are joined tothe adjoining side at an intersection where the strands 22 are helicallywrapped about each other to form interlocking joints 30.

Referring to FIGS. 1A and 1B, the interlocking joints 30 are loose andspaced from each other in the full expansion position. The cells 24 havea diamond shape. The strand angle is α. When the stent 20 is radiallycompressed, in certain instances, the interlocking joints 30 are intight interference such that points 32 and 34 are in close proximity. Inother instances, the interlocking joints 30 separate. In addition, theinterlocking joints 30 on the same circumference are in close contact,therefore establishing the compressed, reduced size which can be fitwithin a sleeve for delivery on a catheter. A medical prosthetic stentand method of manufacturing such a stent is described in U.S. patentapplication Ser. No. 08/743,395 which issued as U.S. Pat. No. 5,800,519on Sep. 1, 1998 and which is incorporated herewith by reference.

Referring to FIG. 2A, an isometric view of stent 10 according to theinvention is shown in an expanded position. The stent 10 is formed froma plurality of strands 42. FIGS. 2C and 2D show enlarged views of twoparts of the stent shown in FIG. 2A. In a preferred embodiment, thereare five strands 42, as seen in the layout view of FIG. 2B. The strands42 are woven in a pattern starting at a proximal end 44. The patternforms a plurality of geometric cells 46. Each strand 42 forms a pair ofsides 48 a and 48 b of the most distal cell 46. Each of the sides, withthe exception of at least one as explained below, are joined to theadjoining side at an intersection 52 where the strands 42 are helicallywrapped about each other to form interlocking joints 54.

While there are five intersections 52, at least one of the intersections52 is formed by strands 42 that cross forming a cross joint and are nottwisted to form a wrap as indicated at point 56 in FIG. 2B. A preferredpattern of where the strands 42 just cross is spaced 1-½ cells 46 away,as seen in FIG. 2B.

The strand angle α is increased in the compressed or constrained stateof the stent in this embodiment. The strand angle can be in the range of10°-80° depending upon the particular embodiment. Smaller strand anglesbetween 10° and 45° often require a shortened cell side length L tomaintain radial expansion force. Cell side lengths L in the range of 0.5to 4 mm, for example, can be used with stent having these smaller strandangles. For stents with larger strand angles in the range of 3-8 mm canbe used, depending on the expanded diameter of the stent, the number ofcells and the desired radial expansion force.

Referring to FIG. 3, the stent 10 is shown in the contracted positionwithin the sleeve 58. Similar to the embodiment shown in FIGS. 1A and1B, the size to which the stent 10 can be constricted is limited bywhere the interlocking joints 54 engage each other. The elimination ofone wrap joint allows for the stent 10 to be compressed to a smallersize.

In a preferred embodiment, the strands 42 are formed of nitinol wire.The wires each have a diameter of 0.006 inches (0.15 mm). The diameterof the wires can vary depending on the number of cells and desiredproperties and generally in preferred embodiments range from 0.004inches (0.10 mm) to 0.006 inches (0.15 mm). The stent 10 has an outsidediameter when fully expanded of 10 millimeters. The stent 10 is capableof compressing into a sleeve 58 of an outside diameter of 8.0 French orless, and preferably 7.0 French (3 fr=1 mm). The stent shown in theFIGS. 1A and 1B, of similar material and dimension, is capable ofcompressing to a diameter of approximately 9 fr.

In one preferred embodiment, the length of the legs or sides 48 of thecells 46 is similar to that of the embodiment shown in FIGS. 1A and 1B.The radial force is decreased from the elimination of one of theinterlocking or wrap joints. The compressed stent 10 has a length ofapproximately 120 percent or less relative to the expanded stent.Therefore, for a 10 centimeter stent, the compressed length is 12centimeters or less.

In one preferred embodiment, the length of the legs or sides 48 of thecells 46 are reduced. The reduced length provides radial force andcompensates for decreased radial force resulting from the elimination ofone of the interlocking or wrap joints. In an alternative embodiment,the radial expansion force increased by varying the anneal cycle of thestent.

The varying of the length of legs or sides 48 of the cell or the changein the angle α can effect foreshortening. While it is preferred to haveforeshortening of 120 percent or less, in certain embodiments it may bedesirable to have greater foreshortening, such as the compressed stent10 has a length of approximately 150 percent of the expanded stent.

In one preferred embodiment, a plurality of (ten shown) platinum-iridiumradiopaque (R.O.) markers 60 are located on the stent 10. The R.O.markers 60 are threaded onto the terminating cells; five on the proximalend and five on the distal end.

A mandrel 62 for making the stent is shown in FIGS. 4A and 4B. Themandrel 62 has a plurality of pins 64 on the outer surface of themandrel in a pattern that determines the geometric cell 46 pattern. Thestrands 42 are bent around the top portion 66 of each top anchoring pin64 to form the proximal end 44 of the stent 10. The strands 42 are thenpulled diagonally downward to an adjacent anchoring pin 64 where thestrands 42 are joined. The strands 42 are helically wrapped about eachother to form the interlocking joint 54, with each strand passingthrough a single 360 degree rotation. The two strands are pulled taughtso that the interlocking joint 54 rests firmly against the bottomportion 68 of the anchoring pin 64 such that each strand 42 ismaintained in tension.

Each level of anchoring pins 64 is missing a pin 64 in a set order, suchas to achieve the desired pattern in FIG. 2B. The stands 42 which passthe missing pin location simply cross to form the cross joint.

In a preferred embodiment, the anchoring pins 64 are square. The squarepins retain the helically wrap of the strands in a proper position. In apreferred embodiment, the pins have a width of 1 millimeter. Theanchoring pins can have a smaller width such as 0.5 mm for use withnarrower diameter strands, such as 0.005 inch diameter strands.

The free ends of the strands 42 are then pulled downward to the nextdiagonally adjacent anchoring pin 64. This process is continued untilthe desired length of the stent 10 is achieved.

The stent 10 is then heat-treated. The strands 42 at the joining end 40of the stent 10 are welded using a ball-welding technique. The strands42 are twisted around each other for several twists of the strands asbest seen in FIG. 2B. The strands having a diameter of 0.006 inches(0.15 mm) will form a diameter of 0.012 inches as seen in FIG. 4C. Inaddition, the ball-weld creates a weld ball 250 having a diameter of0.018 inches (0.46 mm) to 0.020 inches (0.51 mm). Upon compression ofthe stent, the weld balls 250 may engage each other limiting thecompression of the stent. The stent with these diameters can fit withinan outer sheath having a 7 French inner diameter. The heat-treating andalternative finishing techniques are described in U.S. Pat. No.5,800,519 on Sep. 1, 1998, the entire contents is incorporated herein byreference.

A layout view of the distal end of the stent 10 is shown in FIG. 4D. Thestrands 42 of the stent 10 are woven in a pattern as discussed abovewith respect to FIGS. 4A and 4B. The joining ends 40 of the stent 10 arealigned parallel to each other to form the end of the most distal cells46. The joining ends 40 of the strands 42 are held together by a pair ofholding straps 268 onto a surface 270 as seen in FIG. 4E. A laser welder272 moves along the joint 274 of the two adjoining strands 42. Aplurality of energy pulses are directed at the joint 274 as the laserwelder 272 moves along the joint. After completing this initial weld,the laser welder 272 is moved back to a position 280, to achieve afinished length and a higher energy pulse is directed at the point orposition mark by dotted line 280 to cut the strands 42.

In a preferred embodiment, a 400 micron fiber is used with a spot sizehaving a diameter of 3.9 to 4.1 millimeters. In one example, twentypulses of energy are directed at the joint 274 as the laser welder 272moves a distance of 1.3 millimeters (+/−0.5 mm). Each pulse has anenergy level of 145 millijoules (+/−10 millijoules) and a duration of0.1 milliseconds. The single higher energy pulse of one joule, and aduration of 2 milliseconds cuts the strands.

Referring to FIG. 4F, an example of the cross-section of the strands 42using the laser weld technique described above is shown. The laserwelding forms a fill 276 on the top and a cut-off fill 278 on thebottom. The overall diameter of the strands 42 and weld is 0.012 inches(0.3 mm)therein for a five wire system the compression size is 4.57French. Therein, a stent with the laser welded ends can compress to asmaller diameter than those with the ball welds.

Another alternative to the R.O. markers 60 for locating the stent 10using fluroscopy is to coat the stent with gold. The stent 10 can beeither totally or partially coated. In a partially coated stent, onlyportions of the strands between the joints are coated. Coating of astent is described in further detail in U.S. Pat. No. 5,201,901 whichissued on Apr. 13, 1993, the entire contents is incorporated herein byreference. A clad composite stent is described in U.S. Pat. No.5,630,840 which issued on May 20, 1997, the entire contents beingincorporated herein by reference. A further embodiment of the inventionutilizes a stent having a core as described in U.S. Pat. No. 5,725,570which issued on Mar. 10, 1998, the entire contents is incorporatedherein by reference.

In one preferred embodiment, the stent 10 is installed using anendoscope 70 as seen in FIGS. 5A and 5B. The endoscope 70 has a channel72 which is typically used for collecting biopsy samples or for suction.The stent 10 is passed through the channel 72 into the body as explainedbelow. The endoscope 70 in addition has an air/water nozzle 74 forcleaning the area in front of the endoscope 70. In addition, theendoscope 70 has a mechanism for the physician to see what is in frontof the endoscope 70; this mechanism includes an objective lens 76. Apair of illumination lenses 78 which are used in lighting the site arealso shown.

FIG. 5B illustrates a cross sectional view of the distal end of theendoscope 70. An air/water tube 80 extends down to the air/water nozzle74. Both the viewing mechanism and the illumination mechanism haveoptical fiber bundles 82 leading to the respective lens 76 and 78.

Endoscopes come in various sizes and lengths depending on the purpose.The channel 72 likewise has different sizes. It is recognized that itmay be desirable to use a smaller diameter scope to be less invasive orthat a larger diameter scope will not fit the lumen. The following tableis an example of various size endoscopes.

Working Length Distal Tip Channel (cm) O.D. (mm) Diameter (mm) 55 4.82.0 55 6.0 2.6 63 12.2 3.2 102 9.8 2.8 102 12.6 3.7 124 11.0 2.8 12411.0 3.2 125 11.3 4.2 173 13.0 3.2

In a preferred embodiment, with the dimensions given above, the stent 10as described in relation to FIGS. 2A-4B can be used with channels of 3.2mm or greater as described below. It is recognized that with otherdimensions of the stent and/or laser weld of the ends, the stentcatheter can fit in a smaller diameter channels such as 2.6 mm or 2.0mm. For a 2.6 mm endoscope channel, a 2.3 mm outer shaft or catheterdiameter is employed.

In addition, the stent 10 can be introduced using a percutaneousinsertion. In both the method using the endoscope 70 and thepercutaneous procedure, an over the wire delivery system 86 as seen inFIG. 6A can be used. The over-the-wire delivery system 86 has anelongated catheter on inner shaft 88 over which the stent 10 ispositioned. The shaft 88 extends from a proximal handle 90 to a distaltip end 92. The shaft 88 extends through an outer shaft 94 at theproximal end.

An outer sheath 98 is located at the distal end of the over the wiredelivery system 86. The outer sheath 98 is moved towards the handle 90using a pull wire 102 and a pull ring 104 as seen in FIG. 6B. Aguidewire 118 extends through the catheter to the distal end tip 92, asbest seen in FIG. 6A.

In a preferred embodiment, the outer sheath 98 has an outer diameter inthe range of between 0.072 inches (1.8 mm) and 0.094 inches (2.4 mm).The inner diameter of the outer sheath 98 has a range of between 0.066inches (1.7 mm) and 0.086 (2.2 mm)inches. The outer sheath tends to thelower portion of the range when the stent can contract to the 6 Frenchsize and towards the upper portion of the range when the stent cancontract to the 7 French size.

In one preferred embodiment, the outer sheath 98 is formed havingseveral layers of material. The nominal outer diameter is 0.093 inchesand a nominal inner diameter of between 0.078 and 0.081 inches. Theinner layer is composed of polyethylene or TFE and has a nominalthickness of 0.001 inches. A layer of EVA or polyurethane of a nominalthickness of 0.0005 inches forms the second layer. A braid metal springstainless or liquid crystal polymer (LCP) fiber having a thickness of0.0015 to 0.0025 inches overlies the second layer and forms the core ofthe outer sheath 98.

In a preferred embodiment, the fourth layer varies in materialcomposition as it extends from the proximal end to the distal end. Theproximal end of the sheath is formed of Pebax or polyamide and thematerial varies to a polyamide or cristamid at the distal end. Thislayer has a nominal thickness of 0.002 inches. This varying of thematerial is for increased flexibility at the distal end to move throughtortures easier and increased rigidity at the proximal end to give thecatheter better push.

The sheath 98 has a finish layer of a hydrophlic coating having athickness of between 0.0005 and 0.001 inches. The coating is forincrease lubricativity.

The shaft has an outer diameter of 0.074 inches (1.88 mm). The shaft isformed of nylon 12, or cristamid.

In a preferred embodiment, the tip extrusion has an outer diameter inthe range of between 0.042 and 0.055 inches. The inner diameter of thetip extrusion has a range of between 0.036 and 0.040 inches.

In one preferred embodiment, the tip extrusion or catheter has a nominalouter diameter of 0.047 inches and an inner diameter of 0.037 inches.The inner diameter defines the passage for the guidewire. In a preferredembodiment, the catheter is formed of Peek (Polyether ether etherKeetone) Peek Braid Peek, Polyimide or Polyimide Braid Polyimide. In apreferred embodiment, the guide wire 108 has a diameter of 0.035 inches.It is recognized that the guide wire can be larger or smaller asindicated below.

An alternative method to the over-the-wire delivery system 86 shown inFIGS. 6A and 6B is a rapid exchange delivery system 112 shown in FIG. 7.The rapid exchange delivery system 112 has a shaft 114 that extends froma proximal handle 116. A guidewire 118 extends from a two lumentransition zone 120 through an outer sheath 122 to a distal tip end 124.In contrast to the over the wire delivery system 86, the guide wire 118does not extend all the way back to the proximal handle 116. Similar tothe over the wire delivery system 86, the outer sheath 122 of the rapidexchange delivery system 112 is moved towards the handle 116 using apull wire 128 and a pull ring 130.

Referring to FIGS. 8A-8F, the over-the-wire delivery system 86 of FIGS.6A and 6B is shown for positioning a stent 10 in a bile duct. Stents areused in many uses including for treatment of an obstruction 134, such asa tumor in the bile duct. The delivery system can position a prosthesis,such as a stent 10, to move the obstruction out of the lumen 136.

Typically, the occlusion substantially closes off a lumen, such as abile duct which has a healthy diameter of about 8-10 mm. The obstructionmay be several centimeters in length. After the obstruction is locatedusing one of several diagnostic techniques, the physician gains accessto the lumen. Using ultrasound or fluoroscopy, the guidewire 108 such asseen in FIG. 8C, is positioned through the outer access sheath 98 sothat it extends past the obstruction.

Referring to FIG. 6A, the delivery system 86 is advanced axially anddistally until the distal radiopaque marker 140 is positioned axially ata location at least about 1 cm distal of the occlusion 134. Thislocation substantially corresponds to the position at which the distalend 47 of the stent 10, when expanded, will engage the lumen wall 136.The location is selected so the stent 10 is positioned beyond theocclusion 134 but not too close to the end of the bile duct, forexample. The marker 138 indicates the position of the proximal end 40 ofthe stent 10 in the expanded position and is such that the proximal end40 of the prosthesis will engage healthy tissue over a length of atleast 1 cm. Where possible the stent 10 is centered about theobstruction, based on the fully expanded length indicated by markers 138and 140. The marker 139 indicates the proximal end of tile stent whenthe stent is in the fully compact form, which has an overall length ofapproximately 20 percent longer than in its expanded state. Thereforefor a stent of 7.5 centimeters, the compressed state has a length ofapproximately 9 centimeters.

The sheath 98 is retracted in one continuous motion as illustrated inFIG. 8B. With the sheath 98 partially withdrawn, (arrow 144), portionsof the stent 10 expand (arrow 146). The lengthening of the stent 10 hasa simultaneous effect of reducing the radial force the stent exerts onthe wall of the sheath 98 and, therefore, reducing the frictional forcebetween the inner wall of the sheath and the stent 10, allowing asmoother retraction of the sheath 98 with less axial force.

After sheath retraction continues but usually to a point less than themarker 138, the proximal end 40 of the expanding and contractingprosthesis 10 exits the sheath 98 and engages the lumen wall 136,forcing open the lumen 136 to its normal diameter and firmly anchoringthe stent so that it resists axial motion, as illustrated in FIG. 8C.

The stent is released entirely from the catheter body 88 by drawing thecatheter body 88 proximally (arrow 152) as seen in FIG. 8D, which causesthe end loops to be positioned at more distal positions along themembers, until the radial force of the stent 10 causes the members todeflect outwardly (arrows 154).

The catheter 88 is then removed from the body, leaving the prosthesis 10properly positioned as illustrated in FIG. 8E.

An alternative embodiment of the low profile diamond stent is shown as aflat layout view in FIG. 9. The stent 160 has two separate layers 162and 164; an inner layer 162 shown in hidden line and an outer layer 164.Each layer 162 and 164 of the stent 160 has a plurality of strands 166.In a preferred embodiment, each layer has four strands; this is incontrast to the five strands in the previous embodiment. While four andfive strand embodiments are shown above, it is recognized that thenumber of strands and cells can vary, for example, from three to ten orhigher, dependent on size, type of joint or the strands, use and otherfactors.

The strands are woven in a pattern of geometric cells 169 starting atthe distal end 170. Each strand 166 forms a pair of legs 144 of the mostdistal opening on the cell 168. The inner layer 162 and the outer layer164 are intertwined at both the distal end 170 and the proximal end 172.

The sides 176 a, 176 b, 176 c, and 176 d of each of the cells 168 aredefined by a series of strand lengths 178 a, 176 b, 176 c, and 178 d.Each of the sides 176 are joined to this adjoining side at anintersection where the strands are helically wrapped about each other toform interlocking joints 180.

Similar to the embodiment shown in FIGS. 1A and 1B and in contrast tothe previous embodiment, every intersection has an interlocking joint180. Without the fifth strand 166, the stent 160 can be contracted intoa smaller diameter than that of the stent 20 shown in FIGS. 1A and 1B.

In a preferred embodiment for use in a colon, both layers are formed ofidentical materials. Each strand is composed of nitinol and has adiameter of 0.010 inches (0.25 mm).

Still referring to FIG. 9, the two separate layers 162 and 164 in theconstricted position are off-set from each other so the interlockingjoints of one layer do not engage with the interlocking joints of theother layer. The off-set between layers can be created by either anoff-set during manufacturing as described below, or created by therelated motion of the layers as the layers are constricted. The relatedmotion can be the result of the constraints of the strands or thematerial properties. One property difference can be the thickness of thestrands as described in the next embodiment.

The stent can be coated with a silicon lubricant or suitable lubricantto ease the self-expanding of the stent.

An alternative embodiment of the double layer stent 160 of FIG. 9 isshown in FIGS. 10-12. In contrast to the double layer stent 160 of FIG.9, the double layer stent 188 has a cover layer 190 interposed betweenan outer layer 192 and an inner layer 194. The outer layer 192 is shownin hidden line and the cover layer 190 is shown in hidden line in FIG.10. It is recognized that the cover layer 190 can be placed in otherlocations.

Similar to the previous embodiment, the inner layer 194 and the outerlayer 192 are intertwined at both the aproximal end 170 and the distalend 172. The intertwining of the layers 192 and 194 retains the coverlayer 190 in position.

In a preferred embodiment, each layer has four strands and are wovensimilar to the embodiment shown in FIG. 8 to define the geometric cells198. The strands of the two layers are formed of two different thicknesswires in a preferred embodiment. The inner layer has a thicker wire.

FIG. 11 shows the stent in an artery. The stent is moving an obstacleout of the passage. The cover prevents tumor in-growth, will sealfistulas and block aneurysms.

One technique for placing a stent into the circulation system of apatient is to enter from the brachial artery located in the arm. Thispoint of entry can be used for insertion into the vascular systemincluding for example, peripheral locations such as the knee whichrequire the flexibility of the diamond stent.

A cross-sectional view of the stent 188 is shown in FIG. 12. The innerlayer 194 having the thicker strands forces the cover 190 and the outerlayer 192 outward. The cover 190 is in engagement with both the innerlayer 194 and the outer layer 192.

In a preferred embodiment, the strands are formed of nitinol. The innerlayer has strands having a diameter of 0.006 inches (0.15 mm). Thestrands of the outer layer have a diameter of 0.005 inches (0.13 mm).The radial expansion force of the thicker wire inner layer istransmitted to the outer layer. The radial expansion force can bealtered by varying one or both layers.

In another preferred embodiment, the stent has three strands on eachlayer. The inner layer has a diameter of 0.008 inches (0.02 mm). Thestrands of the outer layer have a diameter of 0.005 (0.13 mm) inches.

The outer layer can be formed from a non self-expanding material. Theouter layer can be chosen for its radiopaque characteristics. Materialsthat can be chosen for their radiopacity characteristics includetantalum, platinum, gold or other heavy atomic metal.

In a preferred embodiment, a cover is interposed between the layers. Thecover can be made of several types of material which allow the stent tobe compressed to a small diameter and also be self-expanding. Apreferred material is a woven carbon fiber, a metal mesh, a polymer suchas a polyurethane, or a material treated with a drug for time release.Different agents can be employed on the inside and the outside. Anelectrical current can be applied to tissue using the stent. Differentmaterials for the layers can be used than the interposed cover dependingon the treatment site and the desired method of treatment.

In one preferred embodiment, the layers 192 and 194 are interwoven forthe entire stent without an interposed cover. Referring to FIG. 13, amandrel 262 has a plurality of anchoring pins 264. For a stent havingtwo layers of four strands each, each row has eight (8) anchoring pins264 at the same height. The top row, however, has the anchoring pins 264for one strand positioned ½ millimeter higher than the other set. Afterthe stent is woven, the distal end of each stent is pulled to the sameposition, therein resulting in the rest of the interlocking joints beingoffset.

If there is no cover between the two layers, the two layers can beinterwoven from the distal end to the proximal end.

FIGS. 14A and 14B illustrate a single layer stent 210 having sixstrands. The stent 210 has four wrap joints 254 a pair of cross joints256. FIGS. 14C and 14D show enlarged views of two parts of the stentshown in FIG. 14A.

In one preferred embodiment, the stent 210 has a diameter of 14millimeters in the expanded state. The stent has foreshortening in therange of 12 to 18 percent. With the strands having a diameter of 0.006inches (0.15 mm), the stent with only four wrap joints 254 per row cancompress to fit within a 7 French system.

An alternative delivery system 286 is illustrated in FIG. 15A. The stent10 is positioned over an inner shaft 288, which is a braided tube, at adistal end 289 of the delivery system 286. The inner shaft 288 extendsto a proximal handle 290. The delivery system 286 has an outer shaft 292which extends from the proximal handle 290 to a point 294, which isproximal the distal end 289. The inner shaft 288 extends through a lumen296 of the outer shaft 292 from the proximal handle 290 and projects outat the distal end of the outer shaft 292. The inner shaft 288 secured toa luer fitting 298 housed in the proximal handle 290, also referred toas an actuator housing or gun portion, of the delivery system 286. Theinner shaft 288 is free-floating with the lumen 296.

An outer sheath 300 overlies the inner shaft 288 and the outer shaft 292from the distal end 289 of the inner shaft to a point 302 of thedelivery system 286. The outer sheath 300 is movable relative to theinner shaft 288 and the outer shaft 292 and is pulled from the distalend 289 of the inner shaft 288 using a pull wire 304 which extends in asecond lumen 306 of the outer shaft 292. The distal end of the secondlumen 306 is proximal to the distal end of the lumen 296. The outersheath 300 and the pull wire 304 are pulled using an actuator 308 of thedelivery system 286. The pull wire 304 is attached to a toothed strip310 that engages the actuator 308. A guidewire 312 extends through theinner shaft 288 from the proximal handle 290 to the distal end 289.

In a preferred embodiment, the outer shaft 292 ends between 1.8 and 20.0centimeters before the distal end 289. The outer sheath 300 extends fromthe distal end 289, in the range of 1 to 50 centimeters towards theproximal handle.

Referring to FIG. 15B, an enlarged view of the delivery system where theinner shaft 288 extending from the outer shaft 292 is shown in FIG. 15A.The inner shaft 288 is shown projecting from the lumen 296 of the outershaft 292. The outer shaft 292 narrows at its distal end to minimizelarge discontinuities of material. The pull wire 304 is above the outershaft 292 and can extend around the inner shaft 288. The pull wire 304is carried by the second lumen 306 of the outer shaft 292 to a pointjust proximal to this location. The pull wire 304 extends down and isconnected to the sheath 300 by a pull ring 305. The pull ring 305 in apreferred embodiment is sintered to the outer sheath 300. The innershaft 288 is free to move within the lumen 296 of the outer shaft 292 atthis point.

The distal end 289 of the delivery system 286 is shown enlarged in FIG.15C. At the end of the inner shaft 288 there is located a distal tip318. In a preferred embodiment, the tip is formed of a polymer which hasbeen molded onto the inner shaft 288. Overlying the inner shaft 288 isthe stent 10. The stent 10 is positioned by a reference locator/stop321. The outer sheath 300 overlies the inner shaft 288 and the stent 10,and engages the distal tip 318. A pair of radiopaque markers 328 areshown encircling the inner shaft 288.

Referring to FIG. 16A, a sectional view of the inner shaft 288projecting from the lumen 296 of the outer shaft 292 is shown. The outersheath 300 can be formed of various biocompatible polymers such as apolyamide with a center core of liquid crystal polymer (LCP). It isrecognized that the outer sheath 300 can be formed of other compositionsas discussed above and below in alternative embodiments. In a preferredembodiment, the outer sheath 300 has an outside diameter of 4-7 French.The wall thickness is typically 0.003 to 0.005 inches (0.076 mm to 0.13mm).

The outer shaft 292 has an outer diameter of 0.066 inches (1.7 mm),which allows the proximal end of the outer shaft 292 to fit within theouter sheath 300. The outer shaft 292 in a preferred embodiment is madeof polyamide or nylon, but can alternatively be made of otherbiocompatible polymers such as polyester, polyurethane, PVC orpolypropylene. The lumen 296 of the outer shaft 292 has a diameter of0.035 to 0.037 inches (0.89 to 0.94 mm), for example, and receives theinner shaft 288. The outer shaft 292 in a preferred embodiment has aplurality of other lumens including the second lumen 306 which the pullwire 304 extends through. In a preferred embodiment, the second lumen306 has a diameter of slightly larger than the pull wire 304. The pullwire 304 is typically a single stainless steel wire having a diameter of0.012 inches (0.30 mm). However, the pull wire 304 can consist of aplurality of wires and can be formed of a different material.

The inner shaft 288 is formed of a reinforced layer encased by an outerlayer and an inner layer. In a preferred embodiment, the inner shaft 288has as a center reinforcement layer comprising of a tubular woven steelbraid 320. The reinforcement layer is encased by the inner and outerlayer of polyimide 322. The tubular woven steel braid is formed of flatstrands 324 having a thickness of 0.0015 to 0.003 inches (0.038 mm to0.076 mm) and a width of 0.001 to 0.005 inches (0.025 to 0.13 mm) in apreferred embodiment. The inner diameter of the tubular woven steelbraid is 0.015 to 0.038 inches (0.38 mm to 0.97 mm). The tubular steelbraid is encased in the polyimide such that in a preferred embodimentthe outer diameter of the inner shaft 288 0.021 to 0.041 inches (0.53 to1.0 mm). The thickness of the wall of the inner shaft is typicallybetween 0.003 to 0.008 inches.

Within the inner shaft 288 a guidewire 312 may extend as seen in FIG.16A. The guidewire 312 in a preferred embodiment is formed of stainlesssteel. The guidewire 312 in a preferred embodiment has a diameter in therange of 0.014 to 0.037 inches (0.36 to 0.94 mm) and in a preferredembodiment 0.035 inches (0.89 mm).

Referring to FIG. 16B, a sectional view of the distal end of thedelivery system is shown. The sheath 300 is overlying the inner shaft288 with the stent 10 being interposed. The pull wire 304 seen in FIG.16A is secured to the sheath at a position proximal to that shown inFIG. 16B.

The delivery system 286 can be used in numerous ways. One such way is byplacing the delivery system's outer shaft 292 and inner shaft 288through an endoscope 70 such as shown in FIGS. 5A and 5B. Alternatively,a percutaneous procedure can be used. In both procedures, the guidewireextending through the inner shaft 288 is extended beyond the inner shaft288 and used to define the path. The inner shaft 288 is to be pushed ashort distance along the guidewire. The guidewire and inner shaft 288are moved until the distal tip is in position.

The inner shaft 288 has sufficient strength that it is able to followthe guide wire and resist kinking. Overlying the inner shaft 288 is theouter sheath 300 which gains its structural strength by engaging andforming a continuous structure with the distal tip 318 of the innershaft. The sheath 300 is pulled in the proximal direction to expose thestent 10 as explained above and therefore does not have to slide overthe distal tip 318 of the inner shaft 288.

The stent 10 is located between the outer sheath 300 and the inner shaft288. The inner shaft 288 is secured only at the luer fitting 298 housingthe proximal handle 290 of the delivery system 286. The inner shaft 288floats freely and is not otherwise secured within the lumen 296 of theouter shaft 292.

When the distal tip is in the proper position in the artery, vessel orother desired location, the outer sheath 300 is pulled proximally byusing the handle on the proximal handle 290 which engages an actuator308 that moves the tooth strip 310. The tooth strip 310 is connected tothe pull wire 304 which extends through a lumen in the outer outer shaftto a point beyond the proximal end of the outer sheath and the pull wireextends from that point to the pull ring. With the outer sheath movedproximally, the stent 10 is able to self expand into proper position.

Referring to FIGS. 17A and 17B, an alternative embodiment of a deliverysystem 330 is shown. The delivery system inner shaft 332 which isencircled by an inner ring 338 of a mounting ring 334. The mounting ring334 has at least one radial member or ridge 336, which projects radiallyout from the inner ring 338 towards the outer sheath 300. In a preferredembodiment, the ring 334 has a pair of ridges 336 which project radiallyoutward in opposite directions along a common axis, or in other words,at an angular separation of 180 degrees. Additional ridges 336 that canbe evenly spaced around the circumference of the ring 334 to evenlydistribute the load force on the stent and can extend longitudinallybetween 1 and 8 mm such that the proximal loops at one end of the stentgrasp the ridges during mounting. The stent is then held in place by theouter sheath during delivery and release. For example, three members 336are spaced 120 degrees apart round 334.

Cells of the stent 10 are placed around the protrusions 336. With thestrands 42 of the stent 10 encircling the tabs 336, the stent 10 cancompress while still being retained. Placement of the members at theproximal end of the stent 10 affords maximum extension and compressionof the stent to within the needed diameters.

An alternative method uses a solid mounting ring where the stent is heldwith a friction fit between the outer sheath and the ring to retain thestent in position in the delivery system. The solid ring with thefriction fit is further described in U.S. Pat. No. 5,702,418 whichissued on Dec. 30, 1997, the entire contents of which is incorporatedherewith by reference.

Alternatively, as seen in FIG. 17C, the tabs or ridges 336 of the ring334 retain the stent 10 as the stent 10 is deployed. If it is determinedprior to the stent 10 being totally deployed that the stent is not inproper position, the stent can be retracted back into the deliverysystem.

In a preferred embodiment, the inner ring 334 has an outer diameter of0.05 inches (1.3 mm). The tabs 336 project such that the distance fromthe radial end of one tab 336 to the radial end of a tab on the otherside of 0.07 inches. The tabs have a width of 0.01 inches. The ring 334can have a length of 0.06 inches.

FIG. 18 shows an alternative mounting ring 335. The ring 335 is a solidring with sections removed to define a plurality of grooves 337. Thegrooves 337 receive the strands of the stent 10, with the projections orridges 339 located in the cells of the stent 10.

Similar to the previous “over-the-wire” delivery system shown, an“over-the-wire” delivery system 340 shown in FIG. 19A has an inner shaft342 extending from a proximal handle 344 to a distal tip end 346. Theinner shaft 342 extends through an outer shaft 350 at the proximal end.An outer sheath 352 is located at the distal end of the “over-the-wire”delivery system 340, overlying the exposed inner shaft 342 and a portionof the outer shaft 350. The outer sheath 352 is moved toward the handleusing a pull wire 354 and a pull ring 356. The pull wire 354 extendsthrough a lumen 348 of the outer shaft 350 from the proximal handle 344to a point just proximal to where the inner shaft 342 extends from theouter shaft 350.

Referring to FIG. 19B, the outer sheath 352 is formed of several layersof material. An inner layer 360 can be formed of a nylon 12 whichextends the entire length of the outer sheath 352. Overlying the innerlayer 360 is a braid 362 of either a metallic or fiberglass such as astainless steel braid. The outer sheath 352 has an outer layer 364formed of nylon 12 extending from the proximal end to a positionproximal and adjacent to the distal end 346. The last portion of theouter layer 364 is formed of another material which is less stiff, orsofter, such as a PEBAX.

In a preferred embodiment, the last portion of the outer sheath 352which has the less stiff or softer material on the outer layer 364,extends 36 centimeter (+/−one cm) and the entire length of the outersheath is approximately 200 cm. In a preferred embodiment, the outerdiameter of the sheath is 0.920 inches (+/−0.001 inches, or about 23.4millimeters) with the wall thickness being 0.0070 inches (+/−0.0005inches) (0.1778 millimeter +/−0.0127 millimeter). The braid 362 isformed of a stainless steel having a diameter of 0.0015 inches (0.038millimeter).

It is noted that the delivery systems shown can be used in variouslocations such as non-vascular systems and vascular systems. In theembodiment shown above, one of the application is endoscopic delivery inthe gastric system which requires that the delivery system be capable oftaking a 90 degree bend. The inner shaft, sometimes referred to as thecatheter, has an outer diameter that approximates the inner diameter ofthe outer sheath, for a segment near the distal end, just proximal towhere the stent is positioned, as seen in FIG. 19B. This is in contrastto the embodiment shown in FIG. 16B.

An alternative embodiment of an “over-the-wire” delivery system 370 isshown in FIGS. 20A and 20B. The delivery system 370 has an inner shaft372 seen from the proximal handle 374 to a distal tip end 376. The innershaft 372 extends through an outer shaft 380 at the proximal end. Anouter sheath 382 is located at the distal end of the “over-the-wire”delivery system 370.

This embodiment has the same elements as the previous embodiment. Theouter sheath 382 has variable properties as explained below. Asindicated above, it is recognized that the path the delivery systemtakes is almost never straight and usually has many bends between theinsertion point into the body and the stricture or stent delivery site.In order to reach the delivery site, the delivery system including theouter sheath 382 must be flexible enough to negotiate the bends, buthave sufficient strength and stiffness.

The outer sheath 382 is formed of a plurality of layers. An inner layer390 is formed of a fluorinated polymer such as PTFE or FEP, or polymersuch as HDPE. A second layer 392 (shown in FIG. 20B) encases the firstlayer and consists of a polyurethane such as those sold underneath thename TECOFLEX™ or PLEXAR™. A third layer 394 consists of a polymerbraiding, such as LCP fiber (Vectran), or a metal braided coil. In apreferred embodiment, the braiding is flat. However, it is recognizedthat a round braiding may also be used. A fourth layer 398, an outerlayer, of the outer sheath 382 material properties vary as it goes fromthe proximal end to the distal end.

In a preferred embodiment, the properties of this fourth layer 398 aredivided into two materials and a combination of these materials in thetransition. For example, the first portion is a material/blend chosenfor higher density, crush strength, relative high durometer andstiffness such as a polyamide sold under the trade name Cristamid orHDPE. The material at the distal end being selected for a higherflexibility, crease resistance, such as a polyamide with lower durometeror Pebax material (polyamid elastomer). In a transition area thematerial starts as a high 100 percent of the A property and transitionsto 100 percent of the B property. This transition area in a preferredembodiment is less than one centimeter; however, the transition area canbe up to lengths of 25 centimeters.

FIG. 20B is an enlarged view of the outer sheath 382 extending from thedistal end to the proximal end, with portions broken away. The innershaft 372 and stent 10 have been removed from FIG. 20B to allow greatervisibility of the metal braided coil. The metal braid is formed of aflat wire having a width of between 0.001 inches (0.025 mm) and 0.005inches (0.13 mm) and a thickness of 0.001 inches (0.025 mm). For the LCPfiber braid, the width is 0.003 inches (0.076 mm) and a thickness of0.0007 inches (0.018 mm) diameter. The stiff materials could also bepolyester (PET), LCP (liquid crystal polymer), PEEK, PBT, etc. and thesoft material could be polyester elastomer, Arnitel or Hytrel. Weavepatterns can be one-over-one or two-over-two. The pick density could be20 pick/in or 120 pick/in, or vary in between

While the tailoring of the properties of the outer sheath 382 can bedone for main purpose of ensuring sufficient strength and flexibility.For example, it is desirable that the distal end have sufficientflexibility and still have sufficient hoop or radial strength to preventthe self expanding stent from rupturing the sheath. The tailoring of theproperties can allow the overall wall thickness and therefore the outerdiameter to be reduced.

The dimensions given are for a preferred embodiment. It is recognizedthat the dimension and properties will vary depending on the intendeduse of the delivery system. For example, the overall outer diameter ofthe composite outer sheath 382 could vary from under 3 French (e.g. fora Radius™ (Coronary) delivery system) to 20 French or larger (e.g. for acolonic or aortic delivery system). The wall thickness can vary from asthin as 0.003 inches for example, for coronary use, to as thick as 0.050inches, for example, for colonic or aortic use. In the preferredembodiment described here, the normal thickness is 0.005 inches. It isrecognized that in addition to a seamless transition where the propertyof the outer layer, the fourth layer 398, varies through a transitionportion, the sections can vary more abruptly such as with lap joints.

Referring to FIG. 20C, a sectional view of the distal end of the outersheath is seen. The inner layer 390 has an inner diameter of for examplebetween 0.078 inches to 0.081 inches (1.98 to 2.06 mm) for a 7 Frenchdelivery system. The outer diameter of the inner layer is between 0.082to 0.083 inches (2.1 mm). The second layer 392, which encases the firstlayer 390, has an outer diameter of 0.084 inches (2.1 mm). The thirdlayer with a fiber braid of 0.0007 inches has an outer diameter of0.0868 inches (2.2 mm). The open area of the third layer is filled withmaterial from both the fourth layer and the second layer. The fourthlayer has an inner diameter of between 0.087 inches and 0.088 inches(2.21 mm to 2.23 mm) and an outer diameter of between 0.091 inches and0.092 inches (2.31 mm and 2.34 mm).

The third layer which consists of LCP fiber braid or metal braided coilcould have variable pick density from proximal end to distal end. At theproximal end, the pick density is 20 pick/in for additional stiffnessand tensile strength, and at the distal end, the pick density is 120pick/in for additional flexibility and radial strength to restrain thestent in the delivery system. The transition length can be abrupt orgradual (1 cm to 25 cm).

An alternative embodiment of an “over-the-wire” delivery system 400 isshown in FIG. 21. The delivery system 400 has an outer sheath 402 formedof a plurality of layers. The outer layer as its material propertiesvary as it goes from the proximal end to the distal end.

In a preferred embodiment, the properties are divided into two materialsand a combination of these materials in the transition area. Forexample, the first portion is a material/blend chosen for higherstiffness, crush-strength and having relative high durometer. Thematerial at the distal end being selected for a higher flexibility,crease resistance and with a lower durometer.

In a preferred embodiment, the outer sheath does not have a layercontaining a polymer or metal braided coil.

Referring to FIG. 22A, an alternative embodiment of a stent 410 is shownflat layout. The stent 410 is formed of elongated strands 412 such aselastic metal wires. The wires 412 are woven to form a pattern ofgeometric cells 414. The sides 416 a, 416 b, 416 c, and 416 d of each ofthe cells 414 are defined by a series of strand lengths 418 a, 418 b,418 c, and 418 d. Each of the sides 416 are joined to the adjoining sideat an intersection where the strands 412 in this embodiment are eitherhelically wrapped about each other to form interlocking joints 420 orjoined to form a box node 422. The interlocking joints 420 are discussedabove with respect to FIGS. 2A and 2B.

Referring to FIG. 22B, the box node 422 is formed of a series ofelements. The top of the box node 422 has an interlocking joint 420where the strands 412 which extend from above cross each other. Thestrands 412 then extend down to form the sides of the box node 422. Thestrands 412 then cross each other on the bottom of the box node 422 inanother interlocking joint 420. The respective strands therefore enterand exits the box node 422 from the same side. This is in contrast tothe typical interlocking joint 420 or a cross joint, wherein the strandsenter and exit at opposite corners of the joint. A cross joint isfurther explained above with respect to FIGS. 2A, 2B, and 3. The strands412 are shown representing their path in exploded perspective view. (Theinterlocking joint 420 does not allow the strands 412 to normallyseparate like this.)

The box node constrains the displacement of the cell and introduceslocal stiffness. By varying the number of nodes and location of nodesthe degree of stiffness can be controlled. With this approach, asrequired, the stent can have different local mechanical properties(radial strength, column strength, etc.) without compromisingflexibility. For example, the ends of the stent can be significantlystiffer than the middle portion or vice versa. The node structurerestricts dilation and foreshortening of the stent during flexing,bending, and extension.

FIG. 23A is a flat layout view of another embodiment of the stent 410′.In this embodiment, the stent 410′ has a plurality of joints at the samelevel around the circumference of the tubular stents. The majority ofthe joints are interlocking joints 420. In this embodiment, one of thejoints of the plurality of the joints around the circumference is a boxnode joint 422. The placement of the node joints 422 are located along adiagonal 426 of the stent 410.

FIG. 23B is a flat layout view of an alternative embodiment of the stent410″. In this embodiment, generally two joints of the plurality of thejoints around the circumference is a box node joint 422. The placementof the box node joints are each along a diagonal. The diagonals are atany angle to each other, therefore in certain locations the box nodejoint for each diagonal is one in the same.

FIG. 24A is a schematic of an oblique view of a stent. The strands havebeen removed from FIG. 24B for clarity. The position of the box nodesare shown. In a preferred embodiment, the nodes are on alternatingoblique planes. The nodes are located on opposing oblique planes.Positioning of the oblique planes also constitutes a pattern. The nodesmay be placed on both oblique planes, as illustrated in FIG. 24B, alsowith a repeating pattern.

During deformation (bending, twisting, etc.) the oblique planesaccommodate (dissipates) the transfer of forces and displacementsinstead of simply transmitting the deformation to the next region of thestent. Selecting the planes at opposing angles causes the stent to havea neutral response. Alternatively, the angle can be chosen to yield apreferred bending direction or plane. Locating the nodes on an obliqueplane will cause the nodes to collapse in a staggered manner. When thestent is in a loaded conformation, the nodes will not co-locate in thesame perpendicular plane. This increases the packing efficiency when inits loaded conformation.

A method of making the stent 410 is shown in FIGS. 25A and 25B. Amandrel 432 has a plurality of pins 434 on the outer surface of themandrel in a pattern that determines the geometric cell 436 pattern. Thestrands 412 are bent around the top portion 438 of each top anchoringpin 434 to form the proximal end 440 of the stent 410. The strands 412are then pulled diagonally downward to an adjacent anchoring pin 434where the strands 412 are joined. The strands 412 are helically wrappedabout each other to form the interlocking joint 420, with each strandpassing through a single 360 degree rotation. The two strands are pulledtaught so that the interlocking joint 420 rests firmly against thebottom portion 444 of the anchoring pin 434 such that each strand 412 ismaintained in tension.

Where a box node 422 is desired, the mandrel 432 has a pair of anchoringpins 434 for each box node 422. The strands 412 are helically wrappedabout each other to form an interlocking joint 420 and positionedbetween the anchoring pins 434. The strands 412 extend down the sides ofthe lower anchoring pin 434. The strands 412 are then helically wrappedabout each other to form the interlocking joint 420, with each strandpassing through a single 360 degree rotation. The two strands are pulledtaught so that the interlocking joint 420 rests firmly against thebottom portion 444 of the anchoring pin 434 such that each strand 412 ismaintained in tension.

In a preferred embodiment, the anchoring pins 434 are square with theedges having appropriate radii. The square pins retain the helicallywrap of the strands in a proper position.

The free ends of the strands 412 are then pulled downward to the nextdiagonally adjacent anchoring pin 434. This process is continued untilthe desired length of the stent 410 is achieved. The stent 410 is thenheat-treated. The strands 412 at the joining end of the stent 410 areattached, for example, by ball welding or laser welding the ends of thewires as discussed above.

An alternative stent 450 is shown in a contracted position within thesleeve 452 in FIG. 26A. Similar to previous embodiment, the stent 450 isformed of elongated strands 22 such as elastic metal wires. The wires 22are woven to form a pattern of geometric cells 24. The sides 26 a, 26 b,26 c, and 26 d of each of the cells 24 are defined by a series of strandlengths 28 a, 28 b, 28 c, and 28 d. Each of the sides 26 are joined tothe adjoining side at an intersection where the strands 22 are helicallywrapped about each other to form interlocking joints 460. In contrast tothe previous embodiments, the helically wrapped joints 460 extendlongitudinal in contrast to radial. A medical prosthetic stent withlongitudinal joints and method of manufacturing such a stent isdescribed in U.S. Pat. No. 5,800,519 on Sep. 1, 1998 and which isincorporated herewith by reference.

The strand angle α is increased in the compressed or constrained stateof the stent in this embodiment. The strand angle can be in the range of10°-80° depending upon the particular embodiment. Smaller strand anglesbetween 10° and 45° often require a shortened cell side length L tomaintain radial expansion force. Cell side lengths L in the range of 0.5to 4 mm, for example, can be used with stent having these smaller strandangles. For stents with larger strand angles in the range of 3-8 mm canbe used, depending on the expanded diameter of the stent, the number ofcells and the desired radial expansion force.

In addition to FIGS. 26A and 26B where the joints extend longitudinal,it is recognized that other embodiments such as the box node can extendlongitudinal.

Several delivery systems have been discussed above. It is recognizedthat an alternative delivery system 480, that of a coaxial deliverysystem 480, can be used. Referring to FIG. 27A, a stent 10 is positionedover an inner shaft 482, which is a braided tube in a preferredembodiment at a distal end of the delivery system. The inner shaft 482extends from a handle 484 located at the proximal end. The deliverysystem has an outer shaft 486 which extends from the proximal handle 484to a point, which is proximal to the distal end 488. The inner shaft 482extends through a lumen 490 of the outer shaft from the proximal handle484 and projects out the distal end of the outer shaft. The inner shaft482 is free-floating within the lumen of the outer shaft 486.

An outer sheath 492 overlies the inner shaft 482 and the outer shaft 486from the distal end 488 to the proximal handle 484. This is in contrastto previous delivery systems discussed wherein the outer sheath 492 endsat a point distal to the handle. The outer sheath 492 is movablerelative to the inner shaft 482 and the outer shaft 486 by pulling theouter sheath 492 at the proximal handle end. A guide wire 496 extendsthrough the inner shaft from the proximal handle to the distal end.

Referring to FIG. 27B, a sectional view of the inner shaft 482projecting from the lumen 490 of the outer shaft 486 is shown. The outersheath 492 is coaxial with the inner shaft 482 and the outer shaft 486.The properties of the inner shaft 482, outer shaft 486, and outer sheath492 can be similar to those discussed above with respect to otherembodiments.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A stent delivery system comprising: a catheterhaving an inner shaft with a distal end and a proximal end; an outershaft disposed around the inner shaft, wherein the outer shaft ismovable relatively to the inner shaft; a handle attached to the proximalend of the catheter; a stent concentrically arranged around a distalregion of the inner shaft, wherein a guide wire is disposed in a lumenof the inner shaft; and a sheath extending around the inner shaft andthe stent, the sheath having a composite structure and being coupled toan actuator on the handle with a wire such that the sheath can be movedlongitudinally relative to the inner shaft in response to the movementof the actuator.
 2. The stent delivery system of claim 1 wherein thesheath has a proximal end and a distal end and a material property ofthe sheath varies from the proximal end to the distal end of the sheath.3. The stent delivery system of claim 1 wherein the composite structurecomprises a braid or coil structure.
 4. The stent delivery system ofclaim 1 further comprising a coupling element connected to the outersheath and extending within the catheter from the outer sheath to theproximal end.
 5. The stent delivery system of claim 1 wherein the innershaft has a plurality of concentric layers including a tubular supportlayer and a covering layer over the support layer.
 6. A stent deliverysystem comprising: a catheter having an inner shaft with a distal endand a proximal end, wherein a guidewire is disposed within a lumen ofthe inner shaft; a handle attached to the proximal end of the catheter;an outer shaft disposed around the inner shaft, wherein the outer shaftis movable relatively to the inner shaft; a stent mounting platformextending concentrically around a distal section of the inner shaft,wherein a guide wire is disposed in a lumen of the inner shaft; a sheathwith a proximal end and a distal end, the sheath having a plurality oflayers such that a material property of at least one of the layers ofthe sheath varies from the proximal end to the distal end of the sheath;and an actuator on the handle, the actuator being coupled to the sheathwith a wire such that the sheath can be moved relative to the stentmounting platform with the actuator.
 7. The stent delivery system ofclaim 6 wherein the plurality of layers of the sheath include an innerlayer of a fluorinated polymer, a second layer encircling the innerlayer and comprising a polyurethane, a third layer encircling the secondlayer, and a fourth layer having a varying property material including arelative high durometer material and a relative low durometer material.8. The stent delivery system of claim 7 wherein the third layer is apolymer.
 9. The stent delivery system of claim 7 wherein the third layeris a metal braid.
 10. The stent delivery system of claim 6 wherein thesheath comprises a coiled or a braided structure.
 11. The stent deliverysystem of claim 6 wherein the material property comprises stiffness ofthe sheath, the sheath having a first stiffness along a proximal sectionand a lower stiffness along a distal section.
 12. The stent deliverysystem of claim 6 wherein the first layer comprises a first material andthe second layer comprises a second material different from the firstmaterial.